The overall objective of the proposed research is to identify, characterize and comprehend the neural and hormonal factors controlling the initiation, maintenance and termination of prolactin secretion during the various reproductive states in the rat. The specific objective of the research is to study the unique neuroendocrine reflex involving the repeated and prolonged secretion of prolactin surges which follow a single 60 sec cervical stimulation. Prolactin secretion will be measured by radioimmunoassay. Using hypothalamic surgery and implants of steroids in the brain, attempts will be made to localize the area in which the information derived from cervical stimulation is stored and then retrieved repeatedly to stimulate prolactin surges. The effect of changing photoperiods, hysterectomy, progesterone injections, neonatal androgen treatment, suckling and pelvic neurectomy on the prolactin surges will be determined.